Silent katydid females are at higher risk of bat predation than acoustically signalling katydid males

Males that produce conspicuous mate attraction signals are often at high risk of predation from eavesdropping predators. Females of such species typically search for signalling males and their higher motility may also place them at risk. The relative predation risk faced by males and females in the context of mate-finding using long-distance signals has rarely been investigated. In this study, we show, using a combination of diet analysis and behavioural experiments, that katydid females, who do not produce acoustic signals, are at higher risk of predation from a major bat predator, Megaderma spasma, than calling males. Female katydids were represented in much higher numbers than males in the culled remains beneath roosts of M. spasma. Playback experiments using katydid calls revealed that male calls were approached in only about one-third of the trials overall, whereas tethered, flying katydids were always approached and attacked. Our results question the idea that necessary costs of mate-finding, including risk of predation, are higher in signalling males than in searching females.

发出醒目求偶信号的雄性个体，通常会面临来自窃食性天敌的高捕食风险。此类物种的雌性通常会搜寻发出信号的雄性，而它们更强的运动能力也可能使其面临捕食风险。在利用长距离信号开展求偶的情境下，雄性与雌性所面临的相对捕食风险，此前鲜有研究探讨。本研究结合饮食分析与行为实验发现，无法发出声学信号的雌性螽斯（katydid），相较于发出鸣叫的雄性，面临着来自主要蝙蝠天敌大蹄蝠（Megaderma spasma）的更高捕食风险。在大蹄蝠栖息地下方的捕食残留残骸中，雌性螽斯的数量远多于雄性。利用螽斯鸣叫声开展的回放实验显示，整体仅有约三分之一的试次中，天敌会朝向雄性鸣叫声靠近；而被束缚的飞行螽斯则始终会被天敌接近并攻击。本研究结果对"求偶所需的必要代价（包括捕食风险）在发出信号的雄性个体中高于搜寻配偶的雌性个体"这一观点提出了质疑。